The present invention relates to a needle-selecting apparatus for a knitting machine; in particular, a needle-selecting actuator that activates a piezoelectric finger for needle selection.
In a pattern-knitting machine such as a pattern-knitting circular knitting machine and a pattern-knitting flat knitting machine, a needle-selecting apparatus is used to transmit the pattern-forming procedure stored in a memory device such as a pin drum, tape or floppy disk to a vertical motion of the knitting needle. As an example of such a needle-selecting apparatus, a needle-selecting apparatus for a knitting machine using an electromagnet is known. Due to the functional limitations of the electromagnet, however, there is a limit to how fast the machine can respond. An increase in speed is accompanied by a higher temperature, increased power consumption and an increase in the size of the needle-selecting apparatus itself.
As a variation of this type of needle-selecting apparatus, a piezoelectric needle-selecting apparatus that applies a voltage to a piezoelectric element to operate a finger and thereby select a needle is proposed. According to this piezoelectric needle-selecting apparatus, in an actuator in which the tip of a piezoelectric element that is pasted on both sides of a plate is provided with a finger, an electric voltage is applied to the piezoelectric element via a lead wire, and said finger is operated in such a way that it follows the movement of the piezoelectric element, thereby engaging or disengaging the butt (finger butt) with or from the needle-selecting jack, which is arranged so as to maintain contact with the lower end of the knitting needles.
When a pulse is not applied to the piezoelectric element of the actuator (or when a negative pulse is applied), the tip of the finger comes into contact with the butt (peg) of a jack (or a knitting needle itself) and exerts pressure on the jack. As a result, the butt for raising a cam at the lower end of the jack cannot engage the raising cam, therefore the jack and the knitting needle that comes into contact with the upper part thereof do not undergo a vertical motion. In this case, the knitting needle does not form stitches.
On the other hand, when a pulse is applied to the piezoelectric element of the actuator, thereby causing the piezoelectric element to bend, the tip of the finger does not come within the moving locus of the butt of the jack. The jack, therefore, maintains its perpendicular position. As a result, the butt for the raising cam at the lower end of the jack engages the raising cam, moving the jack and the knitting needle that comes into contact with the jack vertically. In this case, stitches are made by the knitting needle.
Using this piezoelectric needle-selecting apparatus, needles can be selected much faster than in the case of a needle-selecting machine using an electromagnet. The response is quick, and it is possible to apply a higher-cycle pulse. Other benefits include lower power consumption compared with a needle-selecting apparatus using an electromagnet and a significant reduction in the size of the needle-selecting apparatus itself
In such a piezoelectric needle-selecting apparatus, one end of the length of the piezoelectric element is fixed in a cantilevered fashion so as to allow the piezoelectric element to perform a motion. But under the cantilevered method of holding a piezoelectric element, increasing the response speed by applying a high-cycle pulse to the piezoelectric element can make the needle-selecting motion less stable. Moreover, if a ceramic material is used for the piezoelectric element, because ceramic materials are brittle, the piezoelectric element can be damaged by high-speed vibrations.
In order to solve these problems, a method for supporting a piezoelectric element at two points (JP-A-6-169116,  less than 1994 greater than ) and a method for supporting a piezoelectric element at three points (JP-A-5-302251,  less than 1993 greater than ) have been proposed and products based on these ideas are commercially available.
Although it is not apparent from the above publications, the currently available products embodying either of the above patents have fingers that are arranged in a cross-stitched fashion in one row and sixteen stages. As a result, the housing volume has to be large enough to house many stages of fingers, the needles have to be long and two butts need to be established.
The inventors of the present invention have conceived the idea of arranging fingers in two rows and eight stages so that the fingers can be housed in a lower-profile housing, making the whole apparatus more compact. If the height of the housing is small, the needles can be short, and if there are two rows, only one butt suffices. But to ensure the previous level or a higher level of performance using this configuration, a thick piezoelectric element has to be used, and thick piezoelectric elements are prone to breakage as the voltage becomes higher.
The objective of the present invention, therefore, is to improve on the piezoelectric element and its peripherals in a conventional needle-selecting apparatus having a piezoelectric element held in a cantilevered fashion, thereby providing an actuator for needle-selection that is even better than those based on the above-mentioned two-point or three-point support methods.
The present invention is characterized in that, in an actuator using a piezoelectric element in a needle-selecting apparatus for a knitting machine, in which one end of the length of the piezoelectric element is fixed in a cantilevered fashion, a voltage is applied to said piezoelectric element to cause it to move, and the motion is transmitted to a finger that is attached to the forward part of the piezoelectric element, the piezoelectric element has a rear-end mount with its front part tapered towards the piezoelectric element.
Thanks to this configuration, the piezoelectric element does not lose its resilience or flexibility even after repeated bending motions. As a result, the frequency for breakage of the piezoelectric element is reduced. Other advantages are that a thick piezoelectric element can be used, and the height of the housing can be made smaller. By arranging the fingers in two rows and eight stages, the volume of the housing can be reduced by approximately 35% compared with currently sold products.
Preferably, the rear-end mount consists of a front part and a rear part. The front part is made of synthetic resin and is smoothly and linearly tapered towards the piezoelectric element. Preferably, a shallow groove extends between the rear part and the front part of the rear-end mount in the direction perpendicular to the longitudinal direction of the piezoelectric element. The synthetic resin preferably has a hardness of D55 to D85.
The present invention is also characterized in that, in an actuator using a piezoelectric element in a needle-selecting apparatus for a knitting machine, in which one end of the length of the piezoelectric element is fixed in a cantilevered fashion, a voltage is applied to said piezoelectric element to cause it to move, and the motion is transmitted to a finger that is attached to the forward part of the piezoelectric element, the piezoelectric element is fixed to a rear-end mount whose rearmost part is provided with a U-shaped indentation, and in this indentation, an eccentric pin that extends in the direction perpendicular to the longitudinal direction of the piezoelectric element is fitted.
Thanks to this configuration, the angle of the rear-end mount can be adjusted by adjusting the engagement of the eccentric pin and the U-shaped indentation. The position of the rear-end mount can be finely adjusted for a selection of the optimized bending motion. As a result, it is possible to obtain an even vibration amplitude, which leads to a stable finger action and fewer instances of breakage of the piezoelectric element.
The present invention is also characterized in that, in an actuator using a piezoelectric element in a needle-selecting apparatus for a knitting machine, in which one end of the length of the piezoelectric element is fixed in a cantilevered fashion, a voltage is applied to said piezoelectric element to cause it to move, and the motion is transmitted to a finger that is attached to the forward part of the piezoelectric element, one end of the finger is fixed via a pin which is engraved with a spiral groove over practically its entire length.
In this configuration, the spiral groove has functions of preventing friction between the finger and the contact surface, facilitating lubrication and removing foreign matter.
Preferably, the rear-end mount of the finger has a rearmost end provided with a U-shaped indentation, and the piezoelectric element has a front-end mount with its tip press-fitted to this indentation.
The present invention is also characterized in that, in an actuator using a piezoelectric element in a needle-selecting apparatus for a knitting machine, in which one end of the length of the piezoelectric element is fixed in a cantilevered fashion, a voltage is applied to said piezoelectric element to cause it to move, and the motion is transmitted to a finger that is attached to the forward part of the piezoelectric element, the housing that houses this actuator is equipped with a ribbed air-cooling device.
Thanks to this configuration, the temperature of the substrate for driving the piezoelectric element of the actuator can be lowered by approximately 15xc2x0 C., resulting in a reduced frequency of malfunctions and failures of the apparatus.
The present invention is also characterized in that, in an actuator using a piezoelectric element in a needle-selecting apparatus for a knitting machine, in which one end of the length of the piezoelectric element is fixed in a cantilevered fashion, a voltage is applied to said piezoelectric element to cause it to move, and the motion is transmitted to a finger, which is attached to the forward part of the piezoelectric element, at least two unpenetrated tapping holes are provided at a rear wall.
Thanks to this configuration, the rear wall can be lifted by screwing a screw into each tapping holes.